We plan to search for a rheumatoid antigen by studying sera from rabbits immunized with immune complexes from patients with rheumatoid arthritis. We also plan to characterize material in lymphocytes from synovial fluid of patients with rheumatoid arthritis responsible for stimulating autologous peripheral blood lymphocytes. Similarly, we plan to examine material in cell-free synovial fluid from these patients that can also stimulate peripheral blood lymphocytes. In addition, we plan to examine activation of human platelets by immune complex-like material in rheumatoid sera and synovial fluids.